Method of manufacturing a stator assembly for turbomachines



E5, @S7 W. E. HOWALD 3,335,483

METHOD OF MANUFACTURING A STATOR ASSEMBLY FOR TURBOMACHINES originalFiled Dec. 19, 1961 2 Sheets-Sheet l Aug. 15, H937 W- E` HOWALD S METHODOF MANUFACTURING A STATOR ASSEMBLY FOR TURBOMACHINES original Filed Dec.19, 1961 2 Sheets-Sheet if United States Patent O 3,335,483 METHOD OFMANUFACTURING A STATOR ASSEMBLY FR TURBUMACHINES Werner Ernst Howald,Cincinnati, Ohio, assigner to General Electric Company, a corporation ofNew York Continuation of application Ser. No. 366,927, Apr.

3, 1964, which is a division of application Ser. No.

160,669, Dec. 19, 1961. This application Mar. 26,

1965, Ser. No. 444,509

1 Claim. (Cl. 29156.8)

This invention relates to turbomachines, and, more particularly, to amethod for constructing a lightweight, sheet-metal type stator casingfor use in compressors or turbines of such machines. This application isa continuation of my copending application Ser. No. 366,927, filed Apr.3, 1964, now abandoned, the latter being a duly filed divisionalapplication of my original application, Ser. No. 160,669, led Dec. 19,1961.

In airborne turbomachines, such as aircraft-gas turbine jet engines, itis essential that the weight of the engine be kept at a minimum. Asaircraft `are designed for higher ight speeds at greater altitudes,increases in the size of the engine inlet area, and, thus, the engineoverall diameter, have become necessary. A corollary to increasing theengine diameter has been the need for increasing the strength of theouter housing or casing structures, such as the compressor statorhousing. One means for increasing the strength has been to make thecasings from heavier castings, castings (or forgings) being widely usedbecause of their inherent strength and rigidity which enables them toresist the wide range of temperatures and stresses encountered in`aircraft engine applications. However, if a casting, or forging, isused, the housings will usually be much heavier than would be requiredby strength considerations alone because of the minimum thickness of themetal required by the casting, or forging, process. It has, therefore,been recently suggested that stator casings, among other parts of theengine, be made of thin-Walled sheet-metal components which, with properdesign, will not only provide strong, lightweight parts but also willassure the required rigidity of the turbomachine components.

However, the known methods of constructing lightweight sheet-metalstator casings have left something to be desired. Specifically, theyhave required relatively complex structures in order to supply thenecessary rigidity and dimensioning to the light, sheet-metal outerhousing, or shell member. For example, some of the prior art means haveutilized pluralities of rings l-ocated within rings with one or morecross members added to brace the rings one against the other. Furtherproblems which have been experienced by designers of lightweight,sheet-metal components for aircraft jet engines have included the needto compensate for the increased stresses induced by the use of the moreflexible metal parts. One of these problems has concerned the method ofattaching the stator vanes of an axial-flow compressor to the vanesupporting structure, which, in turn, is attached to the outer housing,or casing shell. Another problem has been concerned with ways and meansfor holding the diameter of the outer casing within required limits, yethave the various parts which go to make up the entire compressorstructure iit readily together. Finally, it has usually been necessaryto provide a multiplicity of weldments or braze joints between the manyparts in the prior art sheet-metal structures which has created problemsin structural rigidity and reliability.

Accordingly, a general object of the p-resent invention is to provide amethod of constructing a lightweight, turbomachine stator casingstructure utilizing minimum weight thin-walled, sheet-metal componentswhich provide lCC the casing with high rigidity while, at the same time,aS- sure control of critical dimensions.

It is another object of the invention to provide a method ofmanufacturing a lightweight, sheet-metal turbomachine stator casingassembly having fewer structural parts with increased strength andrigidity while, at the same time, assuring control of criticaldimensions in a flexible, sheet-metal outer casing shell.

A more specific object of the present invention is to provide animproved method of making a casing assembly from a thin-walled,sheet-metal substantially cylindrical outer member and a rigid, innerannular bulkhead member.

Briefly, 'a preferred embodiment of the invention cornprises a method ofmanufacturing a lightweight, thinwalled, sheet-metal aircraft gasturbine compressor assembly, for example, in which the assembly includesrelatively exible, generally cylindrical outer casing member and arigid, fabricated inner bulkhead member, the Casing and bulkhead membershaving pairs of discrete locating surfaces adapted to be placed injuxtaposition, and wherein the nominal inner diameter of the outer(casing) member is machined at the one of the pairs of locating surfacesthereon and the outer diameter of the inner (bulkhead) member ismachined at the `other of the pairs of locating surfaces, the .machineddiscrete pairs of locating surfaces are placed in juxtaposition, `andthe compressor final assembled by fasteners through the pairs oflocating surfaces.

The features of the invention which are believed to be novel are setforth in the appended claim. The invention itself, however, both as toits organization and details, to- -gether lwith further objects andadvantages thereof, will be more readily understood upon reading of thefollowing description in conjunction with the drawings in which:

FIGURE 1 is an axial view of a turbomachine compressor utilizing thepresent invention;

FIGURE 2 is an enlarged cross sectional view taken along line 2 2 ofFIGURE l;

FIGURE 3 is a plan view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a cross sectional view, partially broken away, taken alongline 4 4 of FIGURE 2;

FIGURE 5 is a plan view, partially in cross section, taken along line 55 of FIGURE 2;

FIGUR-E 6 is a cross sectional view yof a casing locating surface; and

FIGURE 7 is a side view of a further embodiment of the invention.

Referring now to the drawings, FIGURE l is an axial View of a compressorstator casing assembly. Indicated generally by numeral 10, in FIGURE l,is an outer sheetmetal shell or casing member. Indicated generally at 12is an inner bulkhead member comprising an outer stator ring 14, aplurality of radially-extending stator vanes 16, and an inner statorring 18. The compressor stator casing is shown as comprising an integralcylindrical structure, however, it is understood that in a preferredembodiment the structure will be split along a horizontal center lineinto two sections. Referring now to FIGURE 2, it will be seen that theouter stator casing is a relatively thin, and flexible, sheet-metalmember supported from within by the inner stator vane and ring assembly,or bulkhead member 12, including the outer ring, indicated at 14, thevanes 16, and the inner ring, indicated at 18. The stator vane and ringassembly alternates with rows of compressor rotor blades, one of whichblades is indicated at 20, in a multistage axial-flow compressorapplication. Although a compressor is used for purposes of illustrationit should be realized that the invention is equally usefulin theconstruction of lightweight turbine stator casing assemblies.

The manner in which the thin-walled, sheet-metal outer casing member isdimensioned and provided with the required rigidity and support will nowbe described. It will be noted that the outer stator ring 14 ischannel-shaped in cross section having two side portions 22-22 extendingupwardly, or outwardly, from a connecting bottom portion 24. The sideportions are generally L-shaped, with the longer portion of the invertedL forming the sides of the channel and each shorter leg forming acylindrical flange 26. The flanges 26-26 extend outwardly of thechannel-shaped stator ring 14 and carry a plurality of locatingsurfaces, or pads 28 on the inner, or under sides thereof.

As stated above, one of the problems connected with known lightweight,sheet-metal type compressor or turbine stator designs has been thetendency for the stator vanes to disengage or be torn away from light,sheetmetal mounting or support structures due to the stress of hightemperature and high llight speed operation. It will be noted that theouter end of the stator vane 16 in FIG- URE 2 projects through theconnecting bottom portion 24 of the outer channel-shaped stator ring 14.Thus, a feature of the present described construction is the provisionwhereby the leading and trailing edges 30 and 32, respectively, of thestator vanes 16 are rigidly secured to the outer stator ring, along theinner surfaces of the side portions thereof at 34 and 36, eachconnection being a single weldment, or brazed joint extending the depthof the channel-shaped ring. Likewise, at the radially inner end of thestator vanes the stator ring 18 may consist of a pair ofinwardly-extending side portions 3838 and a connecting top, or outerportion 40. The inner ends of the stator vanes project through the topportion of the ring, with the leading and trailing edges being rigidlysecured, by welding or brazing, to the inner surfaces of the sideportions 38-38 along the lengths thereof. One of the side portions 38 ofthe inner ring may be extended to provide a support for a rotor sealingmember, such as is indicated at 39, or a rotor bearing means, ifdesired. Thus, in comparison to the known lightweight compressorconstructions, wherein the stator vanes are usually secured at one,point (or perhaps two longitudinally separated points) on the vanecircumference to the vane supporting structure, the constructiondescribed above features a rigidized assembly, including the outer andinner rings and the stator vanes, which assembly features a statorvane-to-ring attachment adapted to reduce the effect of the stressconcentration normally present at the joint between the vane and itssupporting structure.

For ease of assembly the connecting portions 24 and 40 of the outer andinner stator rings, respectively, may consist of axially-split segments,as best shown in FIGURE 5. In this embodiment, the top portion 40 of theinner ring 18, shown for purposes of illustration, is split at 41 ateach vane location. The split line is then cut out at 42 in the generalairfoil shape of the stator vane 16. To firmly secure the vane to thering portion 4t) a collar, or shoe 44 may be utilized, the collar, orshoe also being split to facilitate assembly. Thus, with the vanes 16positioned in the cutouts 42 and the collar halves in abutment, theparts are permanently attached, eihter by welding or brazing, to form arigid, airtight fit. Although utilized in the described embodiment, itwill be understood that use of the collars is not essential as the vanescould simply pierce the ring and be welded, or brazed directly thereto.

It will be seen from the drawings that the outer ends of the leading andtrailing edges of the stator vanes are provided with prolongations48-48, each prolongation being adapted to overlie, or otherwise closelyabut a portion of the outer stator ring. In the embodiment of FIGURES 2and 3 the prolongations overlie the cylindrical anges 26-26 and arepermanently secured thereto. The outer, or upper, surfaces of the vaneedge prolongations comprise a plurality of discrete locating andsupporting surfaces y48a. Likewise, the inner surface 51 of the outercasing member 14, is also provided with a plurality of pads 52 havingsimilar locating surfaces 52a. Each surface 48a on the ring and vane, orbulkhead assembly is adapted to abut a pad surface 52a on the casing,the abutting pads thus comprising pairs of locating, and supporting,surfaces on the inner and outer members, respectively. The pads, orlocating surfaces 52a may be formed from substantially circular metalbuttons, or disks permanently welded or 4brazed to the supportingsurfaces. Additional supporting surfaces, or pads 54 may be permanentlyattached to the outer surface 56 of the sheet-metal casing. Thus, whenin juxtaposition, the surfaces inside the casing, or shell member, andthose on the outer and inner surfaces of the shell member 12 itself,form axially and radially aligned rows of locating surfaces. FIGURE 3perhaps better illustrates the surfaces 48a and the fact that the vaneleading and trailing edge prolongations 48-48 are preferably in the formof small castings permanently aflixed to the vanes 16. FIGURE 3 alsoindicates that stiifening means in the form Aof a plurality of Z-shapedrings 58--58, inserted in sawcuts 59-59 in the outer ends of the hollowstator vanes, may be utilized, although they are not absolutelynecessary. If used, the rings are welded or brazed to the outer surfaceof the ring bottom portion and to the vanes, thus providing additionalrigidity for the inner bulkhead assembly. Clips 60 may also be providedas aids in positioning and holding the rings 58-58 in the sawcuts. Thestator vanes in the embodiment shown in the drawings are preferablyhollow, although they need not necessarily be so, for the purpose ofweight saving. Additionally, when hollow, the vanes may be utilized toconduct cooling air, service air, and/or engine bleed air, in a knownmanner. As stated above, when the described construction is utilized ina multistage compressor there will be a rotor stage, or blade rowalternating with each stator stage, or row of vanes 16. To insure acontinuous ilow path through the compressor, means must be providedadjacent the tips of the row of rotor blades 20 to insure asubstantially airtight channel. In the embodiment shown, a plurality ofshrouds, one of which is indicated at 62, are provided which aresupported in the correct position adjacent the outer stator ring 14 andaxially in line with the bottom, or connecting portion 24 thereof, by amounting llange 64. The flange may have a plurality of discrete locatingsurfaces, or pads 66 attached thereto. These pads are adapted to matewith and abut the discrete locating pads 28 on the inner surfaces of theflanges 26 of the outer stator ring to assure the correct radialplacement of the shroud. The rotor shroud means is assembled with thebulkhead member, as described hereinbelow.

Further sealing means, indicated generally at 68, are provided to assurethat the flow of the compressed air through the machine is continuouslytowards an area of higher pressure, i.e., downstream. This lattersealing means includes a sealing strip 69 attached to the inner surfaceS1 of the casing member 14, the strip extending circumferentiallybetween the pads 52. A similar abutting strip 70 is allxed to the uppersurface of each flange 26. Likewise, abutting sealing strips 71 and 72,respectively, are affixed to the under surface of each llange 26 and tothe mounting llange 64. The pairs of abutting sealing strips `act toprevent backilow from the region of higher pressure downstream of thestator vane and ring assembly 12 I(to the right in FIGURE 2) to theregion of lower pressure upstream thereof (to the left in FIG- URE 2).

It will be apparent from the above description that the inner and outerstator ring and vane assembly, indicated generally at 12, may be termeda bulkhead, or support member for the thin-walled outer casing, or shellmember. In contrast to known arrangements for constructing compressorcasings wherein the stator vanes have solely an aerodynamic purpose, thevanes 16 and the channelshaped inner and outerstator rings 12, inassembly, provide supporting structure sufficient to rigidize athinwalled, flexible, sheet-metal outer casing shell. Thus in accordancewith the primary feature of the invention the inner bulkhead assemblies12 provide critical dimensioning, as well as rigidity, fora sheet-metaltype compressor, or turbine, stator casing-The invention thuscomprehends a novel method of constructing a lightweight compressor, orturbine, stator casing from a substantialy cylindrical sheet-metal outermember and an inner support, or bulkhead member. The method includes thesteps of, first, providing pairs of locating and supporting surfaces,one surface of each pair being on the inside of the outer member, orstator casing 14, and the other surface of the pair being on theoutermost part of the inner bulkhead member 12, or stator vane and ringassembly. In the ydescribed embodiment, these surfaces 52a and 48a areon the pads 52 and the prolongations 48, respectively. The pads 52 maybe formed by brazing, or welding metal buttons or disks on the outercasing member, the surfaces on the bulkhead member being the outermostportion of the prolongation casting 48. Next, the casing is placed in axture and the surfaces 52a of the outer member locating pads 52 machinedto a single diameter. As seen in FIGURE 6, the surfaces 52a of the pad52 will then have an arcuate configuration, in cross section. Next, theouter surface of the pair of locating surfaces, i.e., the surfaces 48aon the leading and trailing edge prolongations, is similarly machined toa single diameter such as to enable the inner stator vane and ringassembly, or bulkhead to be located within the outer casing, -or shellwith the pairs of locating surfaces 52a and 48a in juxtaposition.Finally, the assembly is completed by securing the inner bulkheadassembly to the outer casing shell at the points of abutment of the rowof paired locating surfaces by boring, or otherwise providing a hole 73through the aligned locating surfaces, inserting bolts 74 through theholes and securing the bolts with nuts 75. Obviously, suitable means forattaching the parts described may also consist of rivets or spot welds,within the scope of the invention. Note that the rotor shroud mountingflange may also be secured by the bolt 74 and the nut 75, in oneoperation, the nut preferably being permanently attached to the shroudflange prior to final assembly. With the bulkhead 12 rigidly secured tothe outer casing at the paired locating surfaces, it will be readilyapparent that through close control of the dimensions of the innerdiameter of the casing pads 52 on the outer member and the outerdiameter of the locating surfaces on the inner member, or bulkhead, thatthe compressor casing structure is given extreme rigidity, whilemaintaining circularity and dimensioning, with a minimum of machiningand welding operations. Further, with use of channel-shaped inner andouter rings rigidly secured to stator vane `leading and trailing edgesalong the entire depth of each ring, a rigid structure adapted towithstand the high stresses imposed upon the rows of stator vanes byoperation at high temperatures and high fiight speeds is provided. Incomparision, known lightweight casing structures suffer from extremestresses at the vane-to-ring connections induced by lack of theequivalent of the latter feature, which has often caused such structuresto fail because of vanes tearing free from the mounting structure. Also,by providing, in addition to the constitutent parts of the stator ringsbeing attached to the vanes along their entire abutting surfaces, thatthe vanes themselves are attached- With the rings-directly to thecasing, the -arrangement of the present invention assures that stressesimposed on the vanes are transmitted directly from the vanes to thecasing, through the vane edge prolongations, and not from the vanes tothe vane supporting structure (i.e., rings or channel members) andthence to the outer shell, as has been the previous practice. Thus,with'the vanes (and rings) connected directly to the outer casing andwith a rigid ring and vane, or bulkhead structure inside the casing, theinvention features an improved stator casing construction whereby allthe parts of the assembly, including the thin-walled, flexible outercasing or shell member, even though of lightweight, sheet-metal, act inconcert to provide an extremely rigid, critically dimensioned, strongturbomachine casing structure. With use of the invention it has beenfound that the outer shell can be made yas little as 0.020 inch, orless, in thickness, which is a significant advance in the state of theart of lightweight compressor and/or turbine casing manufacture.

FIGURE 7 illustrates an alternate embodiment of the construction whereinan inner bulkhead member may include a plurality of stator vanes, one ofwhich is indicated at 82, an outer channel-shaped stator ring 83, and aninner channel-shaped stator ring 84. In this embodiment, the statorbulkheads are located and supported on the outer casing by means of asingle vane edge prolongation which may take the form of a casting 85.The casting and the vane trailing edge 86 in this embodiment, aresecurely fastened, by brazing or welding, to the inner surface of a sideportion 87 of the outer stator ring. The prolongation, or casting andthe side portion 87 project radially outward of the compressor statorbeing located between a pair of fianges 88-88 welded to a sheet-metalouter casing 90. At the inner end of the stator vane and ring assemblythere may be provided a pair of cast, or forged annular rings 92-92, towhich are brazed, or welded prolongations of the leading and trailingedges 93 and 86, respectively, and which give rigidity to the inner endof the stator ring and vane assembly and serve as supports for a rotorbearing, or the stationary sealing means indicated at 94-94. Thestructure just described, will also provide rigidity and roundness to athin-walled, sheet-metal stator casing in a similar manner as in thepreviously described embodiment. Control of inner and outer diameterdimensions when manufacturing and assembling the casing according tothis embodiment may be achieved in a number of ways, e.g., by control ofthe dimension of the outer diameter of the flanges 88-88, i.e., thesurfaces 95-95, rand the outer diameter 96 of the vane prolongation 85.When the surfaces 95-95 and 96 are aligned and axial 'holes drilledtherein for receipt of suitable fastening means 98, desired dimensionswill be achieved, as previously described.

While I have described the invention in detail, it will be obvious tothose skilled in the art that various changes and modifications may bemade in the embodiments thereof without departing from the spirit orscope of the invention.

The appended claim which is intended to cover all such modifications andvariations, is as follows:

The method of making -a lightweight aircraft gas turbine casing assemblycomprising the steps of,

forming a sheet-metal cylindrical outer casing,

machining surfaces on said casing having a predetermined axial andradial relationship,

forming a plurality of inner bulkheads, each bulkhead being formed by,

forming a pair of annular sheet metal discs with outwardly bent flanges,

securing to said -annul-ar discs the outer ends of a plurality of statorblades by metal-joining the leading and trailing edges thereof along thewidths of said discs,

securing the inner ends of said stator blades to an annular sheet-metalmember,

machining on said bulkheads a plurality of surfaces having apredetermined axial and radial relationship to said stators andrespectively alignable and registerable with the machined surfaces ofsaid cas- 111g,

assembling said casing and said bulkhead with said machined surfaces inregistered relation, and

7 8 securing together the said registered machined surfaces 2,945,290 7/1960 Walsh 29-156.8 to join the casing to the bulkhead. 2,968,468 1/1961 Walsh 253-78 2,994,508 8/ 1961 Howald 253-7'8 References Cited1,820,069 s/1931 Herr 29-447 X SAMUEL W. ENGLE, Examneh 2,623,728 12/1952 Feilden et al. 253-78 P M, COHEN, Assistant Examiner,

